1. Field of the Invention
The present invention relates to RF paging receivers which receive pages comprised of either numeric characters and/or alphanumeric characters and convey the page to a person possessing the paging receiver.
2. Description of the Prior Art
Paging systems are in use throughout the world. There are paging systems which transmit pages from satellite transmitters to different cities. An example of such a system is that operated by National Satellite Paging which transmits only numeric pages. A system operated by Metrocast permits pages to be transmitted to any city within the system through dedicated communication links between the cities. In the Metrocast system, pages to be transmitted locally are exclusively made by calling into the city where the page is to be made by a local telephone call. A page to be made on a regional basis is called in by an 800 number telephone call to a central facility in San Diego from which the page is transmitted to the city where the page is to be broadcast by the dedicated communication link. The page is received from the communication link at the city where it is to be broadcast and then broadcasted locally by an existing paging service to transmit the page to the person to be paged.
To date, there is no existing national paging system which substantially covers the geographical United States. Because of the cost of hardware, a system like the Metrocast system is not economical in small cities or rural areas where the paging volume is relatively low. Accordingly, while the objective of achieving nationwide paging has been attempted for many years, no existing system integrates local and national paging substantially throughout the geographical United States or throughout the world. The vast majority of paging systems operate totally locally with each system having a limited functionality because of its inability to deliver regional paging. Most paging receivers are tuned to receive only a single channel which inherently limits usage in time frames when heavy paging conditions exist in a local paging system and further prevent usage in other geographical locations where other channel frequencies are used.
Typically each existing paging system has unique specifications which prevents operation of one paging receiver in other systems. For example, the paging receiver identification codes are not universal. Furthermore, existing paging receivers will only receive transmissions from a single type of transmitter (analog or digital) systems. As a result of paging receivers differing in design and operation, the cost of paging receivers is higher as a result of smaller manufacturing volumes than would be realized if a single paging receiver was usable for a worldwide network.
Paging receivers in the Metrocast system cyclically scan a plurality of closely spaced channels to detect the presence of a page for the paging receiver on any one of the closely spaced channels. This paging receiver suffers from the inherent disadvantage that the continual scanning of the closely spaced frequencies requires a substantial power consumption causing the batteries of the pager to have a short life span. Short battery life increases the cost of operation and can cause pages to be lost when the batteries are not promptly replaced.
All paging systems currently issue a paging receiver identification code to each of the paging receivers of purposes of providing a unique identification. There currently is no universal standard for issuing identification numbers to pagers, with the largest system having capacity for issuing only 2,000,000 paging receiving identification codes. Worldwide, there currently are over 12,000,000 pagers in use with projected growth on an annual basis in the paging industry exceeding 20%. Thus, current paging systems do not permit a worldwide paging system to be realized as a result of the actual and projected number of pagers being far larger than the capacity of the identification codes in the largest existing paging system.
All pagers currently monitor the one or more channels which they are designed to receive to detect if a paging receiver identification code accompanying a page on the one or more channels on which they are designed to receive matches a stored paging receiver identification code. If a match exists, then a page is processed and an alarm and a display of the message is made to alert the wearer of the paging receiver of the message contained with the page. These systems transmit the pager identification code in an order of decreasing significance of the digits of the identification code. In other words, if a paging receiver has the identification code 12345, the transmitter precedes the transmission of the page with the sequence of digits 12345. Each pager which receives the channel frequency on which the paging receiver identification code is transmitted continually detects each of the successive digits and maintains its radio frequency receiver on until a mismatch is found between the transmitted and stored paging receiver identification code digits. As a result of the fact that many paging receivers have identification codes in which their more significant digits are common to other paging receivers within a system, a substantial amount of battery power is consumed detecting if a page is intended for a particular paging receiver. Each paging receiver which receives the digits of the paging receiver identification code in an order of decreasing significance is statistically likely to have its radio frequency receiver turned on for most of the transmission of the digits of the paging receiver identification code until the lesser significant digits of the paging receiver identification code are received for the reason that it is the lesser significant paging receiver identification code digits which distinguish one paging receiver from another and only the least significant digit which distinguishes the paging receiver which is desired to receive a particular page from all other paging receivers. Accordingly, the transmission of the paging receiver identification code digits in an order of decreasing significance substantially increases power consumption lessening the life of the batteries of the paging receiver.
Throughout the world different frequency bands have been adopted for transmitting pages. In the United States, transmissions are authorized on VHF and UHF bands. In the United States, the channels of the VHF and UHF bands are separated by 5 KHz steps. Moreover, for each of these bands transmitters are in existence which transmit pages by frequency modulation of a digital carrier wave and other transmitters which transmit pages by frequency modulation of an analog carrier wave. Currently no paging receiver exists which is compatible with transmissions from both analog and digital transmitters. Furthermore, Europe has allocated VHF channels for paging with individual channel frequencies being separated by 6.25 KHz steps and Far Eastern countries has allocated paging channels on a 280 MHz VHF band with individual channels being separated by 2.5 KHz steps. Currently, no paging receivers exist which are operational on any more than one of the above-identified frequency bands. The inability of current paging receivers to receive pages on the different frequency bands allocated throughout the world prevent worldwide paging to be received on a single paging receiver.
None of the commercially marketed paging receivers are programmable by command to receive different channels which severely restricts the paging receivers to usage in limited geographical areas. In the United States there are a large number of paging channels in use in different geographical parts of the country. Because of the fact that the existing paging receivers cannot be programmed by command to receive different channels, it is impossible to universally receive pages throughout the country because of the fact that reception of channels is limited to a single channel fixed upon obtaining the paging receiver from the paging service or to cyclically scan a group of closely spaced channels such as with the paging receiver used by the Metrocast system. Neither approach leads itself to being dynamically usable to accept pages in another geographical area where a different channel or channels are in use. The prior art paging receivers' inability to rapidly change the channels which may be received severely limits the usage of paging for business or other travel.
In the prior art as a consequence of paging receivers being designed to receive only a single channel in a particular frequency band or to scan a sequence of closely spaced channels, antenna gain has not been a problem in achieving reception of pages with sufficient signal strength to permit proper decoding and display of the page. Antenna tuning systems have been used to tune a receiver's antenna in military communication for maximum antenna gain prior to receiving communications. However, these systems do not tune antenna gain dynamically during the reception of the communication. When a paging receiver is used to accept multiple bands of frequencies, environmental characteristics such as variable inductance and capacitance which vary with location, will tend to prevent maximum antenna gain from being achieved especially when the paging receiver is being carried by a person in motion.
Currently, no paging system exists which truly permits paging on a national and international level. This is a consequence of the inability of the paging receivers to receive large number of channels and further the deficiency of the existing systems in having a universal paging receiver identification code which uniquely identifies each of the paging receivers throughout the world with the possibility existing in the current systems of several pagers having the same paging receiver identification code. A universal paging receiver identification code is needed having the capacity to uniquely identify all of the paging receivers throughout the world.
Currently in the United States a relatively small number of channels are used in the large metropolitan areas where most of the paging traffic occurs. As paging traffic increases in view of the relatively small number of channels predominantly in use in metropolitan areas, there is the likelihood that message traffic during the three peak paging periods that occur each day will increase to the point where the predominantly used small number of frequencies will become so busy that it is impossible to rapidly transmit pages to a paging receiver. Because of the fact that current paging receivers are not programmable by remote command to receive pages on different channels, existing networks do not have the ability to dynamically switch channels in large metropolitan areas, when one channel becomes so busy that rapid paging is not possible, to another lesser used channel to eliminate delays in transmitting pages to a paging receiver. In fact, in large metropolitan areas there currently are VHF and UHF mobile channels that are currently under utilized due to the current cellular radio system which could be used as alternative paging channels to receive traffic on commonly used stations.
FM analog and digital paging protocols exist. Existing protocols for the FM analog and digital paging systems do not have a high efficiency in transmitting data per transmitted code. Existing digital transmitters modulate a digital FM transmitter with a binary signal which utilizes frequency shift keying of the basic carrier signal to transmit high levels of a bit with a burst of the shifted frequency and the low level bit with the unshifted frequency of the carrier. Thus, each identifiable digit of the transmission from an FM digital paging transmitter can encode only two distinct levels for each frequency burst of the carrier. Analog FM paging transmitters frequency modulate a sinusoidal carrier with a total of 15 tones to create a hexadecimal value transmitting system in which no modulation of the basic carrier frequency is considered to be the "F" value and the remaining 15 different values are encoded by modulating the FM carrier with distinct tones. Paging receivers which are designed to receive analog transmissions require substantial reception time of each tone to validly detect each character. Thus, while the protocol of FM analog paging transmitters transmits a much higher number of data value for each frequency burst, the slowness of the paging receivers in detecting the discrete tones does not result in a high throughput speed of transmitting characters.
Existing paging systems which permit paging in multiple cities suffer from the deficiency that a long distance phone call is required to phone in a page which is to be transmitted to a remote city. Because of the fact that the long distance phone call is charged to the person wishing to make the page or to the operator of the system (800 service), the expense of using these paging systems is increased and may discourage users from making non-local pages. No national or regional prior art paging system permits a page to be initiated from a geographic area outside the area where the paging receiver is normally located by the making of a local phone call and further for the paging receiver to be programmed to receive the page on a particular channel found at the location where the page is to be received.
Current paging receivers do not execute a repertoire of commands permitting the functional characteristics of the paging receiver to be programmed dynamically by RF transmission. Current paging receivers do respond to commands which provide an alarm to the person wearing the paging receiver that a page has been received such as activating a display and/or providing an audio alarm. However, current paging receivers do not execute a diversity of commands in which the system influences operation and structure of the paging receiver, including commands activating the display to indicate if the page has originated locally or from another region, causing the message transmitted with the page to be stored in a particular memory location in the paging receiver and programming the channels on which the paging receiver is to receive pages and permitting the paging receiver to serve as a relay for pages either to be transmitted or received.
Moreover, the prior art paging receivers do not control the scanning of channels in accordance with a program which automatically causes the RF receiver to monitor the channel on which the last page was received for a predetermined time interval and if no carrier is detected on that channel then scanning one or more additional programmed channels for a predetermined time interval until either a carrier is detected on one of the channels being scanned in which case that channel is scanned for the predetermined time interval or in the absence of any carrier being detected on the one or more channels being scanned shutting down the RF receiver after the predetermined time interval. No prior art paging system is known in which a code is transmitted with the paging receiver identification code to restrict reception of pages in particular geographic areas.
Cellular radio systems dynamically assign channels on which cellular radio receivers are to receive telephone calls. To make or receive a telephone call, a mobile cellular radio is locked onto a set up channel through communications with the transmitter which are established when the cellular radio receiver is turned on. The cellular system then assigns the mobile cellular radio to a specific channel while the mobile cellular radio is making or receiving a telephone call within a cell. As the cellular radio receiver moves from one cell to another cell, the channel is dynamically changed from one channel to another channel to maintain a strong signal channel. A cellular radio receiver does not have a channel memory which stores channels which are to be scanned to establish if a call is forth coming. The dynamic assignment of a channel is initiated by the transmitter for the sole purpose of establishing the channel over which voice communications are to be initiated or to be maintained when moving from one cell to another.
U.S. Pat. No. 4,422,071 discloses a system for programming an identification code of a receiver by a radio frequency communication between a transmitter and the receiver.